Method of manufacturing exhaust aftertreatment devices

ABSTRACT

The present invention provides improved methods of manufacturing modular exhaust aftertreatment devices. One method in accordance with the present invention includes forming subassemblies each defined by a support mat wrapped around a monolith substrate; determining fracture characteristics of each subassembly, which includes maximum and minimum compressive forces; determining a push-in depth for each subassembly based, in part, on the substrate&#39;s dimensions and predetermined gap tolerances of the exhaust aftertreatment devices; soft-stuffing each subassembly into the outer housing according to its respective push-in depth; compressing the outer housing inward to thereby retain the subassemblies within and at least in part by the outer housing, wherein the applied compressive force is between the maximum and minimum compressive forces of the various subassemblies; and sizing the outer housing to eliminate lateral housing growth resulting from compressing the outer housing such that the housing length is substantially equal to a predetermined overall housing length.

CLAIM OF PRIORITY AND CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to U.S. Provisional Patent Application No. 60/986,019, filed on Nov. 7, 2007, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to aftertreatment devices for purification of motorized vehicle emissions, and more specifically to soft-stuffing methods of manufacturing vehicle exhaust aftertreatment devices of modular design.

BACKGROUND OF THE INVENTION

Almost all conventional motorized vehicles, such as the modern-day automobile, include an exhaust system for mitigating the harmful byproducts generated from operation of the vehicle's internal combustion engine. Most exhaust systems include a catalytic converter or similar exhaust aftertreatment device for reducing the toxicity of exhaust gas emissions, and a muffler assembly or similar device for attenuating noise generated by the exhaust emission process. The aftertreatment device is normally placed between the engine exhaust manifold and the muffler of the automobile, but can also be integrated into the muffler assembly itself.

Exhaust aftertreatment devices, such as catalytic converters, normally include one or more monolith substrates, generally of the ceramic honeycomb-type, and a shock-absorbent, insulative support mat surrounding each monolith substrate. The monolith substrate is a catalyst carrier, coated with a catalyst that contains a precious metal, such as platinum, palladium, or rhodium. The precious metal functions to convert noxious or otherwise environmentally unfriendly components of the exhaust gas, such as hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO_(x)), into carbon dioxide (CO₂), water (H₂O) and nitrogen (N). The monolith substrate and support mat are encased within an outer housing, which can be a one-piece or bipartite tube having a cylindrical geometry or other functional shape, fabricated from a metallic substance or other resilient material.

In exhaust aftertreatment devices of this type, the support mat is normally compressed between the outer housing and the monolith substrate. Standard manufacturing specifications generally include a minimum pressure that must exist between the support mat and the monolith substrate such that the monolith substrate is properly retained in place inside the outer housing during normal operation. Correspondingly, the specifications will also establish a maximum, threshold pressure during manufacture because the monolith substrate, which is often comprised of a brittle ceramic material with limited mechanical strength, will tend to fracture along a transverse face thereof under stresses greater than the maximum pressure.

Embedding of the monolith substrate with the surrounding support mat in prefabricated housing tubes can be problematic for an optimal snug-fit seating during operation of the exhaust aftertreatment device. This is due, in part, to prefabricated monoliths and housing tubes that inherently have minor deviations in shape and dimensions. Thus, an excessively tight or an unacceptably loose seating of the monolith substrate and support mat within the tubular housing may result during the fabrication of the exhaust aftertreatment device. An excessively tight seating may lead to rupture of the highly sensitive monolith during, for example, assembly of the exhaust aftertreatment device or installation to the vehicle. In contrast, an excessively loose seating will provide inadequate support for the monolith substrate. Insufficient support may lead to, among other things, displacement and/or shattering of the monolith under loads generated during normal operation, such as, by way of example, vibrations and pulsations of the exhaust gas, as well as excessive, inadvertent solid-borne noise behavior—e.g., impact of the monolith against the metal housing.

SUMMARY OF THE INVENTION

The present invention provides improved methods of manufacturing exhaust aftertreatment devices. The methods disclosed herein ensure a secure and functional fitting of each monolith substrate contained within the device's outer housing, while minimizing or eliminating inadvertent damage or fracture of the monolith substrates resulting from the assembly process. In addition, the present invention offers reduced housing lengths through the active individualization of the outer housing to meet the particular geometry and dimensions of each monolith substrate contained therein.

According to one embodiment of the present invention, a method of assembling an exhaust aftertreatment device is provided. The exhaust aftertreatment device may comprise, for example, a catalytic converter, Diesel Oxidation Catalyst (DOC), Diesel Particulate Filter (DPF), or Selective Catalyst Reduction (SCR) device. The exhaust aftertreatment device includes one or more monolith substrates, one or more support mats, and an outer housing. The method includes the steps of: forming one or more subassemblies, each defined, at least in part, by a monolith substrate wrapped in a support mat; then, positioning each subassembly inside the outer housing; securing each subassembly within the outer housing; and sizing the outer housing such that the housing length is equal to a predetermined overall housing length. The outer housing may be sized by reducing the initial housing length via trimming or shearing the outer housing.

According to one aspect of this particular embodiment, the method also includes determining an individualized push in depth for each subassembly. Each subassembly is then positioned by pushing (e.g., axially soft-stuffing) the subassembly into the outer housing a distance equal to its respective push-in depth. Ideally, the method also includes determining the dimensions of each monolith substrate, such as the width, length, and dimensional deviations of the monolith. In this instance, the push-in depth for each subassembly is determined based, at least in part, upon the dimensions of the respective monolith substrate. Finally, the exhaust aftertreatment device is designed with an array of optimal, predetermined gap tolerances. The gap tolerances include, for example, an inlet-end gap tolerance, an outlet-end gap tolerance, and an inter-monolith gap tolerance. It is desired then, that the push-in depth for each subassembly be based, at least in part, upon the predetermined gap tolerances of the exhaust aftertreatment device.

The method may include additional steps, such as determining a plurality of variable target diameters. The subassemblies are then secured by reducing the outer housing radially inward to thereby compressively retain each subassembly, at least in part, by pressure from the outer housing. The outer housing is reduced inward such that the diameter of the outer housing varies longitudinally in accordance with the plurality of variable target diameters. The outer housing may be reduced radially inward by passing the stuffed outer housing lengthwise through a plurality of selectively positionable sizing rolls. The method may also include the step of determining or gauging certain fracture characteristics of each subassembly. The fracture characteristics may include, for example, a maximum compressive force at which the monolith substrate may fracture or rupture, and a minimum compressive force necessary to securely retain the subassembly within the housing. Accordingly, each of the sizing rolls is operable to selectively apply a variable force that is varied within the range of gauged fracture characteristics

In accordance with another embodiment of the present invention, a method of manufacturing modular exhaust aftertreatment devices is provided. Each of the exhaust aftertreatment device includes at least two monolith substrates, at least one support mat for each substrate, and a generally cylindrical outer housing.

The method includes the steps of: forming a first subassembly defined, at least in part, by a first monolith substrate wrapped in a first support mat; forming a second subassembly defined, at least in part, by a second monolith substrate wrapped in a second support mat; determining distinct push-in depths for each of the subassemblies; pushing or pressing the first subassembly axially into the outer housing a distance equal to the first push-in depth; pushing or pressing the second subassembly axially into the outer housing a distance equal to the second push-in depth; reducing the outer housing inward to thereby compressively retain the subassemblies within and at least in part by the outer housing; and reducing the length of the outer housing such that the housing length is substantially equal to a predetermined overall housing length.

In one aspect of this embodiment, the outer housing is reduced inward by translating the outer housing lengthwise through a number of repositionable sizing rolls that are spaced circumferentially (e.g., in a circle) around an outer periphery of the outer housing. The method may then calculate, gauge, estimate, or otherwise determine certain fracture characteristics for each monolith. The fracture characteristic may include, for example, maximum and minimum compressive forces of each subassembly. The sizing rolls are configured to selectively apply a force to the outer housing that is between the maximum and minimum compressive forces of the first and second subassemblies.

According to yet another preferred embodiment of the present invention, a method of manufacturing a modular exhaust aftertreatment device with predetermined inlet-end, outlet-end, and monolith gap tolerances is provided. The method comprises: providing first, second, and third monolith substrates each having a predetermined length, diameter, and dimensional variations; providing an outer housing having a predetermined optimal overall housing length; providing first, second, and third support mats; forming first, second, and third subassemblies respectively defined by the first, second, and third monolith substrates respectively wrapped in the first, second, and third support mats; determining fracture characteristics for each of the subassemblies including corresponding maximum and minimum compressive forces; determining push-in depths for each subassembly based, at least in part, upon the predetermined inlet-end, outlet-end, and monolith gap tolerances, and the predetermined lengths of each monolith; pushing the first subassembly into the outer housing a distance equal to the first push-in depth; pushing the second subassembly into the outer housing a distance equal to the second push-in depth; pushing the third subassembly into the outer housing a distance equal to the third push-in depth; determining a plurality of variable target diameters based, at least in part, upon the fracture characteristics of the subassemblies; compressing the outer housing radially inward via a plurality of selectively positionable sizing rolls to thereby retain the subassemblies within and at least in part by the outer housing, wherein each of the sizing rolls selectively applies a force that is between the maximum and minimum compressive forces of the various subassemblies, and wherein the plurality of sizing rolls reduces the outer housing radially inward such that the diameter of the outer housing varies longitudinally in accordance with the plurality of variable target diameters; and cutting off at least one end portion of the outer housing such that the length of the outer housing is substantially equal to the predetermined overall housing length.

The above features and advantages, and other features and advantages of the present invention will be readily apparent from the following detailed description of the preferred embodiments and best modes for carrying out the invention when taken in connection with the accompanying drawings and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective-view illustration of exemplary monolith substrates used in fabricating a representative modular exhaust aftertreatment device in accordance with the methods of the present invention;

FIG. 2 is a perspective-view illustration of an exemplary outer housing or canning tube used in fabricating the representative modular exhaust aftertreatment device in accordance with the methods of the present invention;

FIG. 3 is a perspective-view illustration of exemplary support mats used in fabricating the representative modular exhaust aftertreatment device in accordance with the methods of the present invention;

FIG. 4 is a cross-sectional side-view illustration of the representative modular exhaust aftertreatment device with its constituent parts from FIGS. 1-3 properly assembled in accordance with the methods of the present invention; and

FIG. 5 is a flow chart or box diagram illustrating an algorithm or adaptive method of manufacturing or assembling modular exhaust aftertreatment devices in accordance with a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the figures, wherein like reference numbers refer to like components throughout the several views, an exemplary modular exhaust aftertreatment device is shown throughout FIGS. 1-4. The present invention will be described herein with respect to the modular catalytic converter assembly indicated generally as 10 in FIG. 4, which is intended solely as an exemplary application by which the present invention may be utilized or practiced. Accordingly, the present invention is by no means to be limited to the particular configuration or structure of FIGS. 1-4. To that extent, the present invention can be used to assemble assorted exhaust aftertreatment devices, devices of varying geometries, configurations, and compositions, without departing from the intended scope of the claimed invention. By way of example, and not limitation, the methods provided herein can be used to assemble Diesel Oxidation Catalysts (DOC), Diesel Particulate Filters (DPF), and Selective Catalyst Reduction (SCR) devices. The methods provided herein can also be used to fabricate exhaust aftertreatment devices of differing shapes (e.g., rectangular, elliptical, or hexagonal cross-sections), devices having distinct configurations (e.g., varying dispositions) with a fewer or greater number of constituent parts (e.g., more than three support mats, less than three monolith substrates, a bipartite outer housing, housing end bushings, support mat end-seals, etc.).

Referring to FIGS. 1-4, the catalytic converter assembly 10 includes least one, but preferably a plurality of monolith substrates, represented herein by first, second, and third monolith substrates 20, 22 and 24, respectively. The exemplary monolith substrates 20, 22, and 24 are substantially symmetrical and generally cylindrical, honeycomb-type ceramic monoliths, with one or more catalyst materials wash coated, imbibed, impregnated, chemisorbed, precipitated, or otherwise applied thereon. The catalytic converter assembly 10 also includes a generally cylindrical outer housing or canning tube, which is indicated at 30 in FIG. 2. The outer housing 30 has a first, open inlet end 32 and second, open outlet end 34, with a substantially symmetrical, annular central portion 36 therebetween. The outer housing 30 is preferably a unitary or one-piece member, formed from a material of suitable strength and resilience for the intended use of the catalytic converter assembly 10.

The catalytic converter assembly 10 also includes a plurality of support mats, coinciding in number with the number of monolith substrates—in this instance, comprising first, second, and third support mats shown respectively in FIG. 3 as elements 40, 42 and 44. The support mats are preferably substantially identical and generally rectangular in shape, including a respective groove 41, 43 and 45 on one end, and a complimentary tongue portion 47, 49 and 51 on the other, or other combination of complimentary attachment features. As can be seen in FIG. 4, the support mats 40, 42, 44 are wrapped or bound around a lateral or outer peripheral surface 21, 23, 25 of a respective monolith substrate 20, 22, 24, such that the tongue 47, 49, 51 and groove 41, 43, 45 engage and mate, disposing each support mats 40, 42, 44 between the outer housing 30 and a respective monolith substrate 20, 22, 24.

The first, second, and third support mats 40, 42, 44 may comprise a non-intumescent sheet material, an intumescent sheet material, as well as materials comprising a combination of both. By way of example, the support mats 40, 42, 44 can be fabricated from a sheet material containing a vermiculite component that expands from heating in order to maintain sufficient contact between the outer housing 30 and monolith substrates 20, 22, 24 during thermal expansion of the outer housing 30. The support mats 40, 42, 44 are intended to provide resistance to thermal shock due to thermal cycling and to mechanical shock due to impacts and vibrations generated during manufacturing and normal operation of the catalytic converter assembly 10. The support mats 40, 42, 44 also act as an internal heat shield for the outer housing 30.

With reference now to the flow chart in FIG. 5, a method or process of assembling exhaust aftertreatment devices, namely the improved soft-stuffing method of manufacturing exhaust aftertreatment assemblies of modular design in accordance with a preferred embodiment of the present invention is indicated generally at 100. The method 100 preferably includes at least steps 101-123. However, it is within the scope and spirit of the present invention to omit steps, include additional steps, and modify the order presented in FIG. 5. It should be further noted that the method 100 is intended to represent a single operation—i.e., the fabrication and assembly of a single catalytic converter. It is contemplated, however, that the method 100 be applied in a repetitive and systematic manner to produce innumerable catalytic converter assemblies.

The method 100 begins at step 101 with supplying a predetermined number of monolith substrates, such as first, second, and third monolith substrates 20, 22, 24. Step 101 may consist of manually loading each prefabricated substrate into a holding nest or a processing station. In a similar respect, step 103 includes providing a predetermined number of prefabricated support mats, such as first, second, and third support mats 40, 42, 44. Prior to, contemporaneous therewith, or subsequently thereafter, step 105 includes providing an outer housing 30 having an initial length (shown hidden at 60 in FIG. 4 for explanatory purposes) and a predetermined overall housing length, indicated at 68, which will be described in detail hereinbelow. In general, the initial housing length is equal to the cumulative maximum expected lengths of the substrates to be housed therein, plus any clearance and tolerance requirements. Ideally, a scanning device (not shown) will verify that each monolith substrate 20, 22, 24, support mat 40, 42, 44, and outer housing 30 is properly oriented when loaded. In one instance, the scanning device will inspect or scan a shell flow arrow 38 to make sure the outer housing 30 is properly oriented in the “up” position, as shown in FIG. 2, prior to proceeding.

Referring still to FIG. 2, the method 100 also includes measuring, gauging or otherwise determining the individual dimensions of each monolith substrate, as step 107. Ideally, each set of dimensions includes the particular length, diameter, and any dimensional variations (i.e., deviations in shape consistency) of each monolith substrate 20, 22, 24, but may include more or fewer parameters. At step 109, a set of orientation tolerances are determined, namely an inlet-end gap tolerance 76 (a predetermined distance between the inlet end 32 of the outer housing 30 and the first monolith substrate 20), an outlet-end gap tolerance 78 (a predetermined distance between the outlet end 34 of the outer housing 30 and the third monolith substrate 24), and a monolith gap tolerance 80 (a predetermined distance between each of the monolith substrates—i.e., the first and second monoliths 20 and 22, and the second and third monoliths 22 and 24). Notably, steps 107 and 109 can be completed prior to step 101 (e.g., during a quality assurance process in conjunction with the manufacture of each constituent part), or subsequent thereto.

Each of the monolith substrates 20, 22, 24 preferably includes a visible coding, such as first, second, and third bar codes 50, 52, and 54, respectively, as shown in FIG. 1. The bar codes 50, 52, 54 are visibly disposed at a respective outer peripheral surface 21, 23, 25, and encoded with data particular to that substrate. When the first, second, and third monolith substrates 20, 22, 24 are provided (i.e., at step 101), the data contained on each bar code 50, 52, 54 is acquired and stored—e.g., via an automatic reading machine and central processing unit or CPU (not shown).

Subsequent to steps 101 and 103, and at any time prior, during or after steps 105-109, step 111 of FIG. 2 includes forming a number of monolith-mat subassemblies, respectively defined herein, at least in part, by the first, second, and third support mats 40, 42, 44 functionally oriented, wrapped, or bound about an outer peripheral surface 21, 23, 25 of the first, second, and third monolith substrates 20, 22, 24, respectively. For example, an overhead “pick and place” apparatus (not shown) will remove each substrate from its respective holding nest, position it above a wrapping station, and push, press, or place the substrate so as to abut a corresponding support mat retained therein by a mat fixture. A wrap assembly, comprising a center support, a front wrap arm, and a rear wrap arm (none of which are explicitly illustrated herein), functions to complete the wrapping of the mat around the substrate.

After the first, second, and third subassemblies are formed, an electro-mechanical inserter or linear actuator (not shown) functions to move each subassembly (i.e., a monolith substrate wrapped in at least one support mat), to a gauging station (also not shown herein). In this regard, each substrate-mat subassembly is tested or “gauged” to collect data specific to that subassembly and thereby allow for an individualized, accurately targeted gap bulk density (“GBD”). The GBD is the density of the support mat after catalytic converter canning—an indicator of the pressure exerted on the monolith by the mat. According to the embodiment illustrated in FIG. 2, first, second, and third fracture characteristics, respectively comprising a maximum and a minimum compressive force of the first, second, and third subassemblies, are gauged at step 113. Ideally, the maximum compressive force coincides with the pressure at which a respective monolith substrate may fracture or rupture, whereas the minimum compressive force corresponds with the pressure necessary to securely retain that subassembly within the outer housing. The gauging station may include a plurality of hydraulically controlled plungers, a corresponding number of contact plates, a position feedback loop, a funnel guide and a mounting frame. The gauging station will apply a precision-controlled, reduced pressure to each of the first, second, and third subassemblies at a plurality of radial locations, measuring the displaced position values.

Prior to, contemporaneous with, or subsequent to step 113, the method 100 determines, calculates, or establishes a stuffing distance or push-in depth for each of the substrate-mat subassemblies. More specifically, first, second, and third push-in depths 62, 64 and 66, respectively, for the first, second, and third subassemblies, as shown in FIG. 4, are determined. Each push-in depth is based, at least in part, upon the dimensions of the monolith substrate contained within that subassembly (established, acquired, and stored in step 107), and the inlet-end, outlet-end, and monolith gap tolerances, 76, 78 and 80.

Subsequently, each of the subassemblies is placed inside the outer housing 30. More specifically, method 100 of FIG. 5 includes axially soft-stuffing the first, second, and third subassemblies into the outer housing 30. Each subassembly is placed in accordance with its respective push-in depth, at step 117. For example, the linear actuator first engages and advances the third subassembly out of the gauging station, through the funnel guide, and into the outer housing 30 a distance equal to the third push-in depth 66 from a receiving end 33 of the outer housing 30, as seen in FIG. 4. This operation is repeated, translating the second subassembly into the outer housing 30 a distance equal to the second push-in depth 64, and finally stuffing the first subassembly into the outer housing 30 a distance equal to the first push-in depth 62.

Once steps 101 through 117 of FIG. 5 have been completed, a pneumatically-actuated lifter (not shown) raises and relocates the “stuffed” outer housing 30 to a sizing machine (also not shown), where the subassemblies will be operatively secured inside the outer housing 30. Prior to, contemporaneous therewith, or subsequently thereafter, a plurality of variable target diameters (collectively represented herein by diameters 70, 72, and 74 of FIG. 4 for purely explanatory purposes) are calculated, determined, or established in step 119 based, in part, upon the first, second, and third fracture characteristics gauged in step 111. The outer housing 30 is thereafter reduced radially inward at step 121 to thereby compressively retain the first, second, and third monolith substrates 20, 22, 24, at least in part, by pressure from the outer housing 30. For example, a ramming device or similarly functioning apparatus, pushes the outer housing 30 through a sizing head (not shown), comprising a plurality of repositionable sizing rolls or segments (preferably on the order of eight rolls), that are angularly oriented (i.e., circumferentially disposed) about a central axis. Based upon the variable target diameters—e.g., diameters 70, 72, 74 of FIG. 4, determined in step 119, the sizing rolls or segments are selectively radially positioned by, for example, an electric servo-motor (not shown), applying variable pressure to the annular central portion 36 of the outer housing 30, respectively trapping the monolith substrates 20, 22, 24 via the first, second, and third support mats 40, 42, 44. According to the preferred embodiment of the present invention, the variable pressure applied by each roll has a magnitude that is between the maximum and minimum compressive forces of its respective monolith-mat subassembly, as determined in step 113.

Turning now to step 123 of FIG. 5, the outer housing 30 is sized such that the housing length is equal to the predetermined overall housing length 68. Specifically, according to the embodiment presented in FIG. 5, one end portion of the outer housing (represented in FIG. 4 for description purposes by inlet end portion 61 or outlet end portion 63) is cut, sheared, trimmed or otherwise removed at step 123. The outer housing 30 is sized, for example, to eliminate length variations between the individual prefabricated housings, as well as remove lateral housing growth which may result from compressing the outer housing 30 radially inward. It is also within the scope and spirit of the present invention to remove end portions from both sides of the outer housing, including for example, both inlet end portion 61 and outlet end portion 63, in order to accomplish the optimal, overall housing length.

While the best modes for carrying out the invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention within the scope of the appended claims. 

1. A method of assembling an exhaust aftertreatment device including at least one monolith substrate, at least one support mat, and an outer housing, the method comprising: forming at least one subassembly at least partially defined by the at least one monolith substrate wrapped in the at least one support mat; positioning the at least one subassembly inside the outer housing; securing the at least one subassembly within the outer housing; and sizing a length of the outer housing such that the housing length is equal to a predetermined overall housing length.
 2. The method of claim 1, further comprising: determining a push-in depth for the at least one subassembly; wherein said positioning the at least one subassembly includes pushing the at least one subassembly into the outer housing a distance equal to said push-in depth.
 3. The method of claim 2, further comprising: determining dimensions of the at least one monolith substrate; wherein said determining said push-in depth is based at least in part upon said dimensions.
 4. The method of claim 3, wherein the exhaust aftertreatment device has an array of predetermined gap tolerances, and wherein said determining said push-in depth is further based at least in part upon said predetermined gap tolerances.
 5. The method of claim 3, wherein said dimensions include a length, a width, and dimensional deviations of the at least one monolith substrate.
 6. The method of claim 1, wherein said sizing the outer housing length includes reducing an initial housing length via trimming or shearing the outer housing.
 7. The method of claim 1, wherein said securing the at least one subassembly includes reducing the outer housing radially inward to thereby compressively retain the at least one subassembly at least in part by pressure from the outer housing.
 8. The method of claim 7, further comprising: determining a plurality of variable target diameters; wherein the outer housing is reduced radially inward such that a diameter of the outer housing varies longitudinally in accordance with said plurality of variable target diameters.
 9. The method of claim 7, wherein said reducing the outer housing radially inward comprises axially translating the outer housing through a plurality of selectively positionable sizing rolls.
 10. The method of claim 1, further comprising: determining fracture characteristics of the at least one subassembly, said fracture characteristics including at least a maximum compressive force and a minimum compressive force.
 11. The method of claim 10, wherein said reducing the outer housing radially inward comprises axially translating the outer housing through a plurality of selectively positionable sizing rolls, each of said plurality of sizing rolls being configured to selectively apply a variable force to the outer housing that is based at least in part upon said fracture characteristics.
 12. A method of manufacturing modular exhaust aftertreatment devices each having first and second monolith substrates, first and second support mats, and a generally cylindrical outer housing, the method comprising: forming a first subassembly defined at least in part by the first monolith substrate wrapped in the first support mat; forming a second subassembly defined at least in part by the second monolith substrate wrapped in the second support mat; determining a first push-in depth for the first subassembly and a second push-in depth for the second subassembly; pushing the first subassembly axially into the outer housing a distance equal to said first push-in depth; pushing said second subassembly axially into the outer housing a distance equal to said second push-in depth; reducing the outer housing inward to thereby compressively retain the first and second subassemblies within and at least in part by the outer housing; and reducing a length of the outer housing such that the housing length is substantially equal to a predetermined overall housing length.
 13. The method of claim 12, wherein said reducing the outer housing inward includes axially translating the outer housing through a plurality of positionable sizing rolls spaced circumferentially around an outer periphery of the outer housing.
 14. The method of claim 13, further comprising: determining first and second fracture characteristics respectively including maximum and minimum compressive forces of the first and second subassemblies; wherein each of said plurality of sizing rolls is configured to selectively apply a force to the outer housing that is between said maximum and minimum compressive forces of the first and second subassemblies.
 15. The method of claim 14, further comprising: determining a plurality of variable target diameters based at least in part upon said fracture characteristics; wherein said plurality of sizing rolls reduces the outer housing radially inward such that a diameter of the outer housing varies longitudinally in accordance with said plurality of variable target diameters.
 16. The method of claim 12, wherein said determining said first and second push-in depths is based at least in part upon predetermined inlet-end, outlet-end, and intermonolith gap tolerances of the exhaust aftertreatment devices.
 17. The method of claim 16, further comprising: determining dimensions for each of the first and second monolith substrates; wherein said determining said first and second push-in depths is respectively based at least in part upon said dimensions of the first and second monolith substrates.
 18. The method of claim 17, wherein the dimensions of each monolith substrate includes a length, width, and dimensional variations of the monolith substrate.
 19. The method of claim 12, wherein said reducing the length of the outer housing includes cutting off at least one end portion of the outer housing.
 20. A method of manufacturing a modular exhaust aftertreatment device with predetermined inlet-end, outlet-end, and monolith gap tolerances, the method comprising: providing first, second, and third monolith substrates each having a predetermined length, diameter, and dimensional variations; providing an outer housing having a predetermined overall housing length; providing first, second, and third support mats; forming first, second, and third subassemblies respectively defined at least in part by said first, second, and third monolith substrates respectively wrapped in said first, second, and third support mats; determining fracture characteristics for each of said subassemblies, said fracture characteristics including at least maximum and minimum compressive forces; determining first, second, and third push-in depths based at least in part upon said predetermined inlet-end, outlet-end, and monolith gap tolerances, and said predetermined first, second, and third lengths, respectively; pushing said first subassembly axially into said outer housing a distance equal to said first push-in depth; pushing said second subassembly axially into said outer housing a distance equal to said second push-in depth; pushing said third subassembly axially into said outer housing a distance equal to said third push-in depth; determining a plurality of variable target diameters based at least in part upon said fracture characteristics; compressing said outer housing radially inward via a plurality of selectively positionable sizing rolls to thereby retain said subassemblies within and at least in part by said outer housing, wherein each of said sizing rolls selectively applies a force that is between said maximum and minimum compressive forces of said first, second, and third subassemblies, and wherein said plurality of sizing rolls reduces said outer housing radially inward such that a diameter of the outer housing varies longitudinally in accordance with said plurality of variable target diameters; and cutting off at least one end portion of the outer housing such that a length of the outer housing is substantially equal to said predetermined overall housing length. 